As is known, the manufacture of veneers is a production technique for the manufacture of decorative, high-quality surface materials made from real wood. Thereby, in the conventional manufacture of veneers, logs are decorticated, or “de-barked,” then said logs are sawn into halves, thirds, quarters or other parts of a log (so called “flitches”) and are subsequently watered, as a rule, for several days at an increased temperature, in order to prepare them for the subsequent cutting to veneer, the so-called slicing. Then, said slicing process results in veneers having a different thickness, for example veneers having a thickness of approximately 0.5 mm, whereby, dependent on the cutting process, in the obtained product, one distinguishes between the so-called sliced veneer (horizontal or vertical slicing), the so-called peeled veneer (rotary slicing) or the staylog (eccentrical rotary slicing).
Schematically, in perspective views, the widest spread slicing, the horizontally or vertically slicing, is presented in the FIG. 15 to 17. FIG. 15 shows a bisected log 10 which is sliced along the direction of the wood fiber. On the other hand, FIGS. 16 and 17 show a slicing transversely to the fiber direction. Subsequent to said slicing process, a waste board 10 remains which is also termed as “backing board” being shown in FIG. 17. For technological reasons, said backing board cannot be processed to a veneer because the mountings in the cutting equipment cause a waste which cannot be further processed.
Subsequently, the so obtained raw veneer mostly having thicknesses of from about 0.45 mm to 2.5 mm, preferably of from 0.45 mm to 0.8 mm, is dried within some minutes, preferably at temperatures above 100° C. In case of strong corrugation, or “buckling,” said veneer is additionally subjected to a pressing step.
Subsequently, the dried raw veneer is cut to size and is sorted according to qualities. For said cutting to size, high material losses have to be accepted, which can be up to 60%.
Per stroke of the slicer, and after cutting to size, a (sellable) veneer is generated having a surface area of approximately 0.6 m2.
This problem with the manufacture of a veneer which is a precise, however complex and highly wasteful process, is intensified by the fact that the starting material “wood” respectively “tree” is a natural product. Thereby, as a rule, it can not be predicted, whether a log being used for the veneer manufacture results in an acceptable final product veneer. If at all, only very experienced wood purchasers are capable of making reasonably realistic predictions of end product quality. Inclusions, limb rudiments and imperfections in the log are most often unrecognizable, and therefore result in defects in the raw veneer that frequently cannot be accepted for its further processing. All this results in up to 85% material waste generation from the raw material log up to the final product veneer, which has to be accepted in said manufacturing process.
A conventional subsequent working process for the manufacture of a completed surface consists in the assembling of several individual veneer sheets in an assembly factory, or “splicing factory,” and in the subsequent trimming of said assembled/spliced veneer surfaces. As a rule, the assembling/splicing of the veneer sheets is carried out by gluing individual veneer sheets, and, in fact mostly by simultaneously applying heat and pressure, using so called longitudinal or cross feed splicing machines. However, the gluing of the thin and therewith sensitive veneer sheets which cannot be easily handled has proved to be complex, and no striated, thin, linear looking veneers can be manufactured because, for achieving an adequate gluing, the veneer sheets to be assembled have to have a certain minimal width. Furthermore, the local application of heat can affect the wood properties (for example the color), and excess glue must be removed in the region of the glue joints.
Subsequently, the obtained veneer can be applied by gluing onto a substrate, such as a particle board.
The above described process steps are comprised by the so-called “European method” or “North American method” for the manufacture of veneers.
In another technical process, the so-called “Asian method”, said raw veneer is obtained in a thickness of approximately from 0.1 mm to 0.8 mm. After the optional clipping of the edges (lengthwise), the still wet sheets of veneer are applied onto a substrate by means of gluing. Mostly the substrate is plywood. Then, the customers buy the “fancy plywood” and cut out the part of the panel that they need. This results in low yields, as the needed sizes do not necessarily match the size of the plywood panel.
Said Asian style of veneer manufacturing requires an integrated process. The veneer after the slicing of the flitch/block has a high humidity content (above the fiber saturation point). Leaving the sheet laying for a little while creates mold and deterioration of the veneers making them unusable. No storage or transportation over longer distances is possible. Only once the veneer is pressed on the substrate, the product can be transported/handled. The value of the substrate is considerably lower than the veneer itself. Thereby, a veneer product can be economically transported significantly farther than a fancy plywood product. This is particularly important with increasing transport cost.
The precision required to produce these extremely thin veneers is only possible with equipment that can typically produce less than 45 sheets per minute.
Further, the U.S. Pat. No. 3,969,558 discloses the gluing of short pieces of a wooden beam, which subsequently can be sliced. For the gluing, said patent suggests adhesives such as epoxy resin, phenolic resin and resorcinol resin. Said U.S. Pat. No. 3,969,558 aims to avoid the heating/boiling process to be applied in the conventional manufacture of veneers, and suggests, during the whole process, to permanently keep the humidity content of the wood on or above the fiber saturation point. Further, said document suggests that no heating/boiling process takes place prior to the cutting. Therefore, during the whole process, it has to be strictly paid attention that the humidity content of the wood is not decreased, also not short-termed. Finally, said veneer having a thickness between 0.1 and 0.8 mm and a humidity content of more than the fiber saturation point of the wood is overlaid and glued onto a substrate.
The U.S. Pat. No. 3,897,581 discloses the gluing of short, beam-like pieces of wood followed by slicing, whereby the gluing is carried out by the application of a special polyurethane adhesive which also cures in the presence of humidity.
U.S. Pat. No. 3,977,449 discloses a process for the manufacture of wood veneer having a large area and elaborate designed wooden patterns adaptable for mass-production. In said process, a log is sawn or sliced into a plurality of individual flitches which are smoothed on the surfaces and are subsequently glued by an adhesive to form a composite flitch. The composite flitch is subsequently sliced to form a sheet of wide wood veneer which may be glued to a substrate or a veneer by means of an adhesive. Throughout the process, all steps are carried out while the wood is maintained at a humidity content at or above the fiber saturation point of the wood. Also the humidity content of the obtained veneer is kept at or above the fiber saturation point.
Besides the conventional manufacture of veneers, so-called technical veneers are also known. In manufacturing said veneer type, it is aspired to achieve a constant quality and a dimensional accuracy in order to be able to better predict the characteristics of the final product veneer.
In this context, for example, conventionally manufactured peeled veneers, optionally after a pretreatment such as dyeing or baking of structures, are glued to each other, and the so obtained material is subsequently re-sliced. Thereby, a veneer surface can be created having a mostly predetermined surface structure, and the material waste can be reduced. However, the so obtained veneers are, concerning their surface, by no means comparable with a normal veneer surface, because the obtained final product has an artificial aesthetic, and does not give the impression of real wood. It is also obvious that such processes are comparatively complex.
The invention is based on the problem to improve the processes for the manufacture of veneers currently known such that, starting from the original employed raw material wood, a high yield of the high-quality final product veneer can be achieved with minimal complexity. Thereby, on the one hand, the process should be kept as simple as possible, and on the other hand, the further processing of the obtained veneer should be facilitated for the user, for example, the manufacturer of furniture. Furthermore, in the veneer, the aesthetics of the used real wood should be maintained. In addition it was the objective to use standard equipment of the European style veneer manufacturing process, in particular slicers allowing slicing speeds in excess of 90 sheets per minute.